Conventional drive guide apparatuses of this type are disclosed in Japanese Patent Post-Exam Publication No. Hei 7-106053 and Japanese Patent Application Unexamined Publication (KOKAI) No. 2001-99151. FIG. 1 is a diagram showing schematically the arrangement of a conventional drive guide apparatus of the type described above.
In the figure, a linear motor 100 comprises a primary side 101 and a secondary side 102. The primary side 101 is an energized side including armature coils. The secondary side 102 is a non-energized side having magnets, etc. The primary side 101 is connected through a table 103 to moving blocks 105 each serving as a moving member of a guide mechanism 104. The secondary side 102 of the linear motor 100 is secured to a base 106. The base 106 is secured to the top of a surface plate 107.
The base 106 is provided thereon with two parallel rails 108 constituting the guide mechanism in combination with the moving blocks 105. The moving blocks 105 move along the rails 108 in response to driving force obtained from the linear motor 100.
The rails 108 are each formed with a plurality of rolling element rolling surfaces extending longitudinally, as will be detailed later. The moving blocks 105 are each formed with endless recirculation passages including load rolling element rolling passages corresponding to the rolling element rolling surfaces. When the moving blocks 105 move along the rails 108, a plurality of rolling elements arranged and accommodated in the endless recirculation passages roll and recirculate while receiving a load in the load rolling element rolling passages.
In the drive guide apparatus arranged as stated above, the table 103 secured to the moving blocks 105 to extend therebetween is provided with the primary side 101 of the linear motor 100, which is the energized side including armature coils. Therefore, when a driving electric current is passed through the armature coils (not shown) of the primary side 101, heat generated from the primary side 101 is transferred to the table 103, causing the table 103 and the moving blocks 105 to be heated to expand. Consequently, stress due to the thermal expansion of the table 103 and the moving blocks 105 is applied to the moving blocks 105.
The rolling elements arranged and accommodated in the endless recirculation passages of the moving blocks 105 constituting the guide mechanism 104 have been given a predetermined preload. More specifically, rolling elements having a diameter slightly larger than the diameter of the load rolling element rolling passages are inserted into the rolling passages, thereby producing a negative clearance, i.e. causing the rolling elements and the rolling surfaces to be elastically deformed.
When stress due to thermal expansion is applied to the moving blocks 105 as stated above, the preload is varied. That is, the preload increases at one side and decreases or becomes zero at the other side. The increase in the preload involves the problem that the rolling resistance to the rolling elements increases, leading to shortening of the lifetime of the drive guide apparatus.
Here, let us explain the preload. The preload is applied in order to ensure a predetermined rigidity adequate for each particular purpose. In apparatus that are required to exhibit high accuracy, e.g. precision measuring apparatus, a light preload necessary for removing play is applied because the apparatus cannot perform the desired function if there is play. In machine tools or the like, an intermediate preload is applied in order to ensure the required rigidity because a cutting operation and the like cannot be performed unless the rigidity is sufficiently high.
It should be noted that rigidity includes static rigidity and dynamic rigidity. Static rigidity is the ability to resist a static load, i.e. a displacement of the moving block relative to the mounting reference plane. Dynamic rigidity is performance required for machine tools, for example, which is expressed by the reciprocal ratio of the deflection width of a time-varying displacement to the deflection width of a time-varying load. In short, dynamic rigidity is the ability to minimize external vibration transmission. That is, insufficient dynamic rigidity of a machine tool, for example, causes chatter during cutting or other machining process and leads to a problem that the machine tool is readily affected by external vibration.
The above-described conventional example has a rolling guide arrangement in which the moving blocks 105 each serving as a moving member are engaged with the rails 108 through rolling elements. It should be noted, however, that the above-described problems also occur in the case of employing a slide guide arrangement in which rolling elements are not interposed between a rail and a moving member. In this case also, the lifetime of the guide apparatus is shortened.
In the rolling guide, an increase in rolling resistance gives rise to a problem. In the case of slide guide, an increase in sliding resistance becomes a problem.
The present invention was made in view of the above-described circumstances. An object of the present invention is to provide a drive guide apparatus capable of ensuring an increased lifetime by preventing heat generated from a primary side of a linear motor from being transferred to a rail or a moving member of a guide mechanism to which the primary side of the linear motor is connected, thereby preventing variation of rolling resistance of the guide mechanism (when arranged in the form of a rolling guide) or sliding resistance of the guide mechanism (when arranged in the form of a slide guide).